Synergistic Chemical Looping Process Coupling Natural Gas Conversion and NO<i>_x</i> Purification

Abstract

We present a novel low-temperature chemical looping combustion scheme for simultaneous natural gas conversion into a sequestration-ready CO 2 stream and NO x purification. The scheme employs nickel oxide (NiO) supported on ZrO 2 as the oxygen carrier. In the process, CH 4 reduces the oxidized carrier to Ni/ZrO 2 in a co-current moving bed reactor, which is then oxidized back to NiO/ZrO 2 by the NO x -laden flue gas in a fluidized bed reactor, completing the oxygen carrier loop. Thermodynamic studies demonstrate that the presence of CO 2 does not significantly affect NO x purification performance at different flue gas flow rates. The operating temperatures of the reactors are selected based on NO x -temperature programmed oxidation (TPO) and CH 4 -temperature programmed reduction (TPR) experiments. Results show that the process can optimally operate at temperatures close to the combustion plants’ flue gas temperature of 400–500 °C, reducing the need for hot utilities. The study conducts comprehensive isothermal and autothermal analyses of the process to evaluate the effects of temperature and carrier flow rate on CH 4 conversion, CO 2 selectivity, carbon deposition, and NO x conversion. For the autothermal analysis, the CH 4 reactor operates adiabatically, while the NO x reactor operates isothermally. Comparative studies with the conventional NO x selective catalytic reduction (SCR) process indicate an exergy efficiency and effective thermal efficiency (ETE) improvement of 9 and 18 percentage points, respectively. The findings suggest that this low-temperature chemical looping process is a promising solution for flue gas NO x treatment, utilizing cheaper natural gas as the reductant and eliminating environmental concerns, such as ammonia or urea slippage. Overall, this study contributes to the development of more efficient and sustainable methods for reducing NO x emissions.

Topics & Concepts